1. Field of the Invention
Example embodiments of the present invention relate generally to reverse link power control in a wireless communications network.
2. Description of the Related Art
A cellular communications network typically includes a variety of communication nodes coupled by wireless or wired connections and accessed through different types of communications channels. Each of the communication nodes includes a protocol stack that processes the data transmitted and received over the communications channels. Depending on the type of communications system, the operation and configuration of the various communication nodes can differ and are often referred to by different names. Such communications systems include, for example, a Code Division Multiple Access 2000 (CDMA2000) system and Universal Mobile Telecommunications System (UMTS).
UMTS is a wireless data communication and telephony standard which describes a set of protocol standards. UMTS sets forth the protocol standards for the transmission of voice and data between a base station (BS) or Node B and a mobile or User Equipment (UE). UMTS systems typically include multiple radio network controllers (RNCs). The RNC in UMTS networks provides functions equivalent to the Base Station Controller (BSC) functions in GSM/GPRS networks. However, RNCs may have further capabilities including, for example, autonomously managing handovers without involving mobile switching centers (MSCs) and Serving General Packet Radio Service (GPRS) Support Nodes (SGSNs). The Node B is responsible for air interface processing and some Radio Resource Management functions. The Node B in UMTS networks provides functions equivalent to the Base Transceiver Station (BTS) in GSM/GPRS networks. Node Bs are typically physically co-located with existing GSM base transceiver station (BTS) to reduce the cost of UMTS implementation and minimize planning consent restrictions.
FIG. 1 illustrates a conventional communication system 100 operating in accordance with UMTS protocols. Referring to FIG. 1, the communication system 100 may include a number of Node Bs such as Node Bs 120, 122 and 124, each serving the communication needs of UEs such as UEs 105 and 110 in their respective coverage area. A Node B may serve a coverage area called a cell, and the cell may be divided into a number of sectors. For ease explanation, the terminology cell may refer to either the entire coverage area served by a Node B or a single sector of a Node B. Communication from a Node B to a UE is referred to as the forward link or downlink. Communication from a UE to a Node B is referred to as the reverse link or uplink.
The Node Bs are connected to an RNC such as RNCs 130 and 132, and the RNCs are connected to a MSC/SGSN 140. The RNC handles certain call and data handling functions, such as, as discussed above, autonomously managing handovers without involving MSCs and SGSNs. The MSC/SGSN 140 handles routing calls and/or data to other elements (e.g., RNCs 130/132 and Node Bs 120/122/124) in the network or to an external network. Further illustrated in FIG. 1 are conventional interfaces Uu, Iub, Iur and Iu between these elements.
A fractional power control scheme has been proposed for controlling the mobile or UE transmission power on the reverse link of the 3GPP LTE standard. This open loop fraction power control technique proposes setting the UE transmit power spectral density such that a fraction of the path loss (including shadowing) may be compensated. Namely, the UE transmit power spectral density TxPSD_dBm may be established as:TxPSD_dBm=min(Max—TxPSD_dBm, Target—SINR_dB+PathLoss_dB+UL_Interference_dBm)   (1)where                Max_TxPSD_dBm is the maximum UE transmit power spectral density (power per tone), which is a function of the UE power class and the assigned transmission bandwidth (for example, the 21 dBm UE power class assigned a single resource unit of 12 subcarriers will have a maximum transmit power per tone of 10.21 dBm);        UL_Interference_dBm is the reverse or uplink interference measured by a Node B serving the UE (typically, this the Node B determines this as total received energy minus the energy received from UEs being served by the Node B), and is reported to the UE, for example, over a control channel;        PathLoss_dB is the path loss between the Node B and the UE; and        Target_SINR_dB is the target signal-to-noise ratio (SINR) per antenna per tone. The fractional power control scheme available in the literature sets the target SINR to be a function of the path loss to the serving cell as follows:Target—SINR_dB=A+(B−1)*(PathLoss_dB)   (2)        where A and B are design parameters. Ignoring the Max_TxPSD_dBm limitation in (1), the UE transmit power spectral density is given by:TxPSD_dBm=A+B*PathLoss_dB+UL_Interference_dBm   (3)Note that if B=0, there is no compensation for the path loss and all UEs transmit with the same transmit power spectral density (possible maximum power), which results in high interference levels and poor cell edge performance. If B=1, this is traditional slow power control in which the path loss is fully compensated and all UEs are received with the same SINR. This results in poor spectral efficiency. By setting 0<B<1, only a fraction of the path loss is compensated, which provides flexibility in balancing spectral efficiency and cell edge performance.        